Immunochromatography is a rapid detection/diagnosis technique, and is typically classified into sandwich and competitive immunochromatographic assays. The mechanism for sandwich immunoassay is as follows: a specific antibody is firstly immobilized to a zone (line) of a nitrocellulose membrane and the like (i.e., a chromatographic membrane) in a test paper; after one end of a sample pad in the test paper is immersed in a liquid sample (e.g., urine, serum, milk, etc.) or alternatively the liquid sample is added to one end of the sample pad, the sample moves towards the other end along the nitrocellulose membrane under capillary action; when the sample moves to the zone (line) immobilized with the antibody, a corresponding antigen in the sample will specifically bind to the antibody; and then this zone may develop a certain color or emit fluorescence by means of immunocolloidal gold technique, immunoenzymatic staining or immunofluorescence technique, thereby achieving specific immunological diagnosis and detection. On the other hand, the mechanism for competitive immunochromatographic assay, which is used for detecting small molecules, can be described briefly in two cases as follows: when a small molecule conjugate is immobilized to the nitrocellulose membrane, the binding of a small molecule to be detected to a free antibody makes it impossible for the free antibody to bind to the small molecule conjugate on the nitrocellulose membrane, that is, the small molecule to be detected competes with the small molecule conjugate on the nitrocellulose membrane for opportunity to bind to the free antibody; and when a specific antibody is immobilized to the nitrocellulose membrane, the small molecule to be detected competes with the free labeled small molecule for opportunity to bind to the specific antibody immobilized to a specific zone of the nitrocellulose membrane. Then, the presence or absence of the analyte is determined according to decreased or disappeared color or fluorescence of the zone to which the small molecule conjugate or the specific antibody is immobilized.
During the above detection, the color or fluorescence is observed or evaluated with the naked eye or a detection instrument in qualitative, semi-quantitative and quantitative manners. At present, the immunochromatographic technique and such technique-based test paper products have been widely applied in the fields such as medical detection and food safety inspection.
Traditional immunochromatographic test strips made on the basis of this technique typically comprise the following components: a backing and a sample pad attached to the backing, a conjugate pad (the conjugate pad for label), a cellulose membrane, an absorbent pad, and the like. When detection is carried out, once a sample is added drop-wise onto the sample pad, the sample migrates on a chromatographic strip in the sample pad under capillary action. During the migration, the sample reacts specifically with a label on the conjugate pad to produce an immunocomplex; and the immunocomplex continues to migrate and specifically binds to the corresponding antigen/antibody in the detection region of the cellulose membrane to form a visible or detectable band.
The above-mentioned immunochromatographic test strips in traditional reaction mode usually have the following technical drawbacks:
(1) During the drying of the conjugate pad which is produced by means of immersion or spraying, owing to the action of “edge effect”, the reagents such as labels on the conjugate pad are rendered unevenly distributed.
(2) When a sample flows through the sample pad and the conjugate pad, there is random error to a certain degree for the amount of the reagents which are released from the conjugate pad and participate in the reaction, due to the randomness of the flow pattern and of flow-through time of the liquid, in particular when there is a snap.
(3) The change in the ambient temperature has some influences on the reaction.
(4) The immunochromatographic test strips in traditional reaction mode is generally in a form having a snap, and thus it is inconvenient to stop reaction by a way of removing the sample pad, and it is prone to cause the results to have a relatively large error, due to the difference in reaction time when observed.
(5) When the results are evaluated with the naked eye, difference may occur due to the different environmental lighting, personal vision, and personal evaluation criteria.
The above technical drawbacks lead to or exacerbate error of results, especially when such technique is used for quantitative and semi-quantitative detection.
At present, there are improved immunochromatographic test strips which have been developed to overcome the above drawbacks, for example, the test strips in “reaction vessel (micropore)+test strip” mode, which do not comprise the sample pad/conjugate pad. The improved immunochromatographic test strips have relatively more advantages over the test strips in traditional reaction mode, but they still have drawbacks including excessive operation steps and troublesome application. Typically, a single detection comprises the following 5 steps: 1. adding a sample into the reaction vessel and mixing it homogenously; 2. incubating the reaction vessel for a period of time; 3. inserting the test strip into the reaction vessel and allowing for reaction in the incubator for a period of time; 4. taking out the test strip, and removing the sample pad, thereby stopping the reaction; and 5. placing the test strip in a reader to read the results. Such cumbersome operation steps are disadvantageous to rapid on-site detection in terms of efficiency and simplicity, which is obvious especially for clinical detection. Therefore, there is a need to provide a device capable of performing a rapid immunochromatographic assay.